Pin Nock and Arrow Stiffness

tabashir

Supporter
Supporter
Hi folks,
I heard somewhere but can't remember where, that swapping over from G-Nocks to Pin nocks will stiffen an arrow.
I'm curious why this is.
I understand that adding a heavier point will weaken an arrow as it is adding inertia to the end furthest from the point where the propulsion is applied so the shaft may be forced to bend a little more to accommodate.
I can also understand that it will alter the FOC of the arrow as marginally more weight is added to the tail end.
I can also get that the arrow, now being heavier will lose some speed due to the energy from the string/limbs being the same meaning that if the mass changes, the velocity must also change.
So is the arrow acting stiffer purely down to this reduced velocity due to weight, or is there another factor I'm missing that will make it act stiffer?
 

dvd8n

Supporter
Supporter
AIUK Saviour
I think that the factor that you are missing is that moving weight around on the arrow shaft affects the positions and intensity of the nodes and antinodes created on the arrow shaft when it vibrates.

So the arrow oscillates differently when it is shot and this makes it appear to act stiffer or weaker as it 'snakes' it's was around the riser in a different manner.
 

Stretch

Active member
Just to be clear, it’s not a big difference. If your arrows are weak and you slap in a pin nock they’ll still be weak. So in my current setup my clearance is not great, the tail of the arrow is very close to the rest and button. With Beiter Over Nocks I regularly damage lower hen vane. With Beiter pin nocks my clearance is better - might still trash the vane on a bad shot.

Along with the adding mass to the back of the arrow also remember that you are replacing a hollow tube of plastic with a solid aluminium pin so the back 1cm or so of the arrow is a lot stiffer. That section probably doesn’t bend at all so in terms of dynamic spine probably makes stuff all difference but it is stiffer :)

I‘ll leave it to one of the physics folks to explain why weight on the front weakens/ weight on the back stiffens. But it is the way.

Stretch
 

dvd8n

Supporter
Supporter
AIUK Saviour
I've always found the effect to be barely noticeable as long as you keep the arrows the same length.
 

deg

Member
Hi folks,
I heard somewhere but can't remember where, that swapping over from G-Nocks to Pin nocks will stiffen an arrow.
I'm curious why this is.
I understand that adding a heavier point will weaken an arrow as it is adding inertia to the end furthest from the point where the propulsion is applied so the shaft may be forced to bend a little more to accommodate.
I can also understand that it will alter the FOC of the arrow as marginally more weight is added to the tail end.
I can also get that the arrow, now being heavier will lose some speed due to the energy from the string/limbs being the same meaning that if the mass changes, the velocity must also change.
So is the arrow acting stiffer purely down to this reduced velocity due to weight, or is there another factor I'm missing that will make it act stiffer?
The string is pushing the arrow from behind. Intuitively, if you add weight at the front, the whole shaft has to push against a heavier point and bends more (i.e. weaker dynamic spine) - a pin nock adds weight behind the shaft, so more of the string force goes to accelerate the heavier pin-nock set and less along the shaft toward the point - so less force to bend the shaft => shaft appears stiffer.

The effect is (as others said) minimal tho!

Gianc.
 

tabashir

Supporter
Supporter
Thanks Gianc.
I already had some nock pins and pin nocks so I ran a very brief test at 30m. I had my normal 29.5" 560 ACCs with XS Wings and small G-Nocks, a couple of bareshaft G-Nocks and a bareshaft with nock pin.
The nock pin one was set up as G-Nock replaced with a nock pin inserted into the bushing rather than replacing the entire bushing as well. This elongates the arrow by around 1.5mm to nock groove and by my calculations adds about 4 grains to the back end.
I shot 3 fletched for the group then the bareshafts with nock pin one always second of the three. I wasn't shooting as well as I'd like but repeated several ends with similar results. Normal bareshafts were within the group where the nock pin ones were consistently around 6 inches to the left (ie stiff).
For comparison, with my setup, if I change a stiffness bracket (using the Easton charts), the bareshafts would be at very least 18" off the group likely nearer 24". I know this because I have tested with 1916 Plats. These were actually shafts I was hoping to stiffen up with the nock pins so that I could interchange them (alongside plunger). Clearly this won't work!
Also for comparison, when tuning 1/12 of a turn of the limb tiller bolts (eg 12 o'clock to 1 o'clock) makes around 3" movement in the bareshaft so adding the pin nock would give me around the same as 1/6 turn of tiller bolts.
So it does, albeit with limited testing show exactly what you all have been saying in this thread, namely that adding a bit of weight to the back in the form of pin nocks does make the arrow act stiffer. To Stretch's point, it won't be enough to make a very weak arrow good, but it is a little something that you can tweak if, for example you just need a little extra because your limbs won't adjust any more.
 
  • Like
Reactions: deg
Top